The present invention relates generally to a projection optical system, and more over particularly to a catadioptric projection optical system that projects and exposes an object, such as a single crystal substrate and a glass plate for a liquid crystal display (“LCD”), using a mirror. The present invention is suitable, for example, an immersion exposure apparatus (an immersion lithography exposure system) for exposing the object through a fluid between the projection optical system and the object.
The photolithography technology for manufacturing fine semiconductor devices, such as semiconductor memory and logic circuit, has conventionally employed a reduction projection exposure apparatus that uses a projection optical system to project and transfer a circuit pattern of a reticle (or mask) onto a wafer, etc. The recent, more highly semiconductor device (circuit pattern) require stricter specification and performance for a projection optical system. Generally, a shorter wavelength of the exposure light and/or a higher numerical aperture (“NA”) is effective to improve resolution. Recently, an optical system with 1 or more of NA by an immersion optical system that fills a space with fluid between a final glass surface (in other words, the lens arranged at most wafer side) of the projection optical system and the wafer has been proposed, and further higher NA progresses.
With a short wavelength of the exposure light ranging such as an ArF excimer laser (with a wavelength of approximately 193 nm) and a F2 laser (with a wavelength of approximately 157 nm) and the like for higher resolution, lens materials are limited to quartz and calcium fluoride for reduced transmittance. An optical system that includes only lenses (refracting element) uses, generally, quartz and calcium fluoride when the exposure wavelength is 193 nm for instance. However, the quartz and calcium fluoride are small differences in their dispersion values, and have difficulties in corrections to chromatic aberrations, especially, for the optical system that has very higher NA like the immersion optical system. Moreover, lens materials larges an aperture along with higher NA, and increases an apparatus cost. Various proposals that uses a mirror for an optical system have been made to solve the disadvantageous reduced transmittance, difficult chromatic aberrations corrections and large-aperture of lens materials (see, for example, Japanese Patent Application, Publication No. 2002-83766, Japanese Patent Application, Publication No. 8-62502, Japanese Patent Application, Publication No. 2002-182112). For example, a catadioptric projection optical system combining a catoptric system and a dioptric system has been disclosed in Japanese Patent Application, Publication No. 2002-83766 and Japanese Patent Application, Publication No. 8-62502. An example of adopting the catadioptric projection optical system to prevent the increase of the apparatus cost has been disclosed in Japanese Patent Application, Publication No. 2002-182112.
In configuring a projection optical system that includes the catoptric system with a shorter exposure wavelength and a higher NA, it is necessary to adopt an optical system that enables chromatic aberration corrections, obtains a large enough imaging area on an image surface, and feasible for further higher NA. Especially, when NA is higher further than about 1.1, an object-to-image distance (in other words, a distance between the reticle and the wafer), and an effective diameter of lens materials becomes very large. Therefore, neither an enlargement of the optical system nor the increase of the apparatus cost are avoided.
An optical system shown in FIG. 13 of Japanese Patent Application, Publication No. 2002-83766 and an optical system shown in FIGS. 7 and 9 of Japanese Patent Application, Publication No. 8-62502 are a three-time imaging catadioptric optical system for forming an intermediate image twice. It includes a first imaging optical system for forming a first intermediate image of a first object (e.g., a reticle), a second imaging optical system that includes a concave mirror and forms a second intermediate image from the first intermediate image, and a third imaging optical system for forming the second intermediate image onto a second object surface (e.g., a wafer). The second imaging optical system includes concave mirrors as a reciprocating optical system (double-pass optical system).
The optical system with an NA of 0.75 in FIG. 13 of Japanese Patent Application, Publication No. 2002-83766 arranges a plane mirror (reflection block) near the first and second intermediate images, and aligns optical axes of the first and third imaging optical system with each other. Thus, the first object and the second object are arranged in parallel. However, such an optical system considerably enlarges when NA becomes 1 or more such as the immersion optical system, especially, about 1.1 or more. Because the first imaging optical system from the first object to near the plane mirror and the third imaging optical system from near the plane mirror to the second object are arranged on a straight optical axis, a sum of the object-to-image distance of the first imaging optical system and the object-to-image distance of the third imaging optical system becomes the the object-to-image distance (the distance between the reticle and the wafer) of the entire optical system. It is necessary to strong a refractive power of each lens to prevent the enlargement of the optical system according to a higher NA, and the aberration correction becomes difficult. Moreover, because a reduction magnification larges by the first imaging optical system, the first intermediate image larges NA of the first intermediate image for an object side NA in the first object at only the reduction magnification. As a result, an incidence angle range and the maximum incidence angle to the plane mirror increase, and it becomes a serious problem for further higher NA by the immersion etc. In other words, the incidence angle range and the maximum incidence angle to the plane mirror considerably increase, and a deterioration of an imaging performance is not avoided by an influence of a deterioration of plane mirror characteristic etc. Because the plane mirror is arranged near the second intermediate image, the second intermediate image is also similar.
An optical system with NAs of 0.45 to 0.5 in FIGS. 7 and 9 of Japanese Patent Application, Publication No. 8-62502 is similarly a catadioptric projection optical system for forming an image three-times or an intermediate image twice. In this optical system, neither the first object (reticle) nor the second object (wafer) are a position relationship of the parallel. The imaging performance in a scanning exposure can be improved, and a stability performance can be maintained by arranging the first object and the second object in especially vertically for gravity and in parallel. Therefore, it is undesirable to develop an exposure apparatus that has the optical system with a higher NA by the immersion etc. that neither the first object nor the second object are the position relationship of the parallel. This optical system needs another plane mirror to arrange a first object and a second object in parallel. In that case, as described in Japanese Patent Application, Publication No. 2002-83766, a mirror provides the same arrangement as the optical system in FIG. 13 of Japanese Patent Application, Publication No. 20002-83766 if arranged near the first intermediate image. A paraxial magnification of the first imaging optical system or the second imaging optical system is the reduction magnification, and is allotted to a paraxial magnification of entire system. If such power arrangement is composed, the incidence angle range and the maximum incidence angle to the plane mirror arranged near the second intermediate image increase, and a light separation of light near the first intermediate is difficult, for further higher NA, especially, NA over 1 by the immersion. Moreover, because the reciprocating optical system (double-pass optical system) includes only the concave mirror and a negative lens, an incidence angle of a principal ray that enters the plane mirror arranged near the second intermediate image inevitably considerably increase more than 45 degrees, and the maximum incidence angle to the light that enters the plane mirror considerably increases.
In the optical system in FIG. 13 of Japanese Patent Application, Publication No. 2002-83766 and the optical system in FIGS. 7 and 9 of Japanese Patent Application, Publication No. 8-62502, because an absolute value of the paraxial magnification is small, a pupil position of the first imaging optical system is nearer the first intermediate image than the first object. Therefore, if the plane mirror is arranged in the first imaging optical system, the distance from the first object to the plane mirror becomes long, and the distance between the first object and the second object becomes long. As a result, the problem that the object-to-image distance that is the distance from the first object to the second object becomes long is caused.
On the other hand, an optical system in Japanese Patent Application, Publication No. 2002-182112 uses a beam splitter, is a three-time imaging catadioptric optical system that uses an i-line for a light source, and arranges one common beam splitter at the pupil position on a common optical axis of the first imaging optical system and the second imaging optical system. However, a fabrication of a beam splitter that achieves an optical performance demanded along with a higher NA by the immersion and further shorter wavelength such as ArF excimer laser and F2 laser is very difficult and leads to the cost-up. For example, in the optical system with 1.1 or more of NA, an effective diameter of lens material near the pupil of final imaging optical system considerably increases, the beam splitter enlarges, and such space is not easily secured in the optical system. Moreover, because a thickness of the lens material composed the beam splitter becomes very thick, the deterioration of the image performance by an exposure aberration is feared. In the optical system that used the beam splitter like the above references, it is very difficult to arrange the first object (reticle) and the second object (wafer) in parallel.